1. Field of the Invention
The present invention relates to a motor driving device and an electronic appliance and a vehicle using such a motor driving device.
2. Description of the Related Art
FIG. 8 is a block diagram showing a conventional example of a motor driving device. The motor driving device 100 of the present conventional example is a semiconductor device that drives a motor 200 through a high-voltage resistant driver 300. In the motor driving device 100, an external resistor 400 is used to generate, from phase voltages U, V and W, voltage-division phase voltages VU, VV and VW and a neutral point voltage Vref, then small low-voltage resistant comparators 110U, 110V and 110W with small variations in offset are used to compare the voltage-division phase voltages VU, VV and VW and the neutral point voltage Vref for each phase and thus the rotational position of a rotor is detected from the back electromotive force of the motor 200 without use of a sensor.
Examples of the conventional technology related to what has been described above includes JP-A-2012-80690 and JP-A-2008-193812.
However, in the motor driving device 100 of the conventional example described above, since the three comparators 110U, 110V and 110W are used as a means for comparing the voltage-division phase voltages VU, VV and VW and the neutral point voltage Vref, the size of the motor driving device 100 is increased and hence its cost is increased.
Moreover, in the motor driving device 100, since the external resistor 400 is used as a means for generating, from the phase voltages U, V and W of the motor 200, the voltage-division phase voltages VU, VV and VW and the neutral point voltage Vref, the number of components is increased and hence its cost is increased.
In the motor driving device 100, the phase voltages U, V and W are divided with reference to a ground voltage GND. Since in the external resistor 400, there are relatively small variations in resistance value, the accuracy of detection is unlikely to be reduced; however, as described above, disadvantageously, the number of components is increased and hence its cost is increased. On the other hand, although when the external resistor 400 is integrated into a semiconductor device, the number of components is reduced and hence its cost can be decreased, since there are large variations in resistance value as compared with the external resistor 400, the accuracy of detection is disadvantageously lowered significantly.